Convert to using ExitStack instead of nested. (#21329)

* Convert to using ExitStack instead of nested.

nested is not available in Python3.

* Use ExitStack from contextlib2.

ExitStack has not been backported to the Python 2.7 standard library and
contextlib.nested is no longer available in Python 3.5.  We need to be
able to use something in both 2 and 3 as we transition so we'll pull in
contextlib2 which has backports of the full python3 contextlib.

common/lib/xmodule/xmodule/modulestore/tests/utils.py

@@ -5,7 +5,8 @@ from __future__ import absolute_import
 
 import io
 import os
-from contextlib import contextmanager, nested
+from contextlib import contextmanager
+from contextlib2 import ExitStack
 from importlib import import_module
 from shutil import rmtree
 from tempfile import mkdtemp
@@ -255,7 +256,7 @@ class StoreBuilderBase(object):
     @contextmanager
     def build(self, **kwargs):
         """
-        Build the modulstore, optionally building the contentstore as well.
+        Build the modulestore, optionally building the contentstore as well.
         """
         contentstore = kwargs.pop('contentstore', None)
         if not contentstore:
@@ -419,7 +420,8 @@ class MixedModulestoreBuilder(StoreBuilderBase):
         """
         names, generators = list(zip(*self.store_builders))
 
-        with nested(*(gen.build_with_contentstore(contentstore, **kwargs) for gen in generators)) as modulestores:
+        with ExitStack() as stack:
+            modulestores = [stack.enter_context(gen.build_with_contentstore(contentstore, **kwargs)) for gen in generators]
             # Make the modulestore creation function just return the already-created modulestores
             store_iterator = iter(modulestores)
             next_modulestore = lambda *args, **kwargs: next(store_iterator)

requirements/edx/base.in

@@ -34,6 +34,7 @@ boto==2.39.0                        # Deprecated version of the AWS SDK; we shou
 boto3==1.4.8                        # Amazon Web Services SDK for Python
 botocore==1.8.17                    # via boto3, s3transfer
 celery==3.1.25                      # Asynchronous task execution library
+contextlib2                         # We need contextlib2.ExitStack so we can stop using contextlib.nested which doesn't exist in python 3
 defusedxml
 Django<1.12                     # Web application framework
 django-babel-underscore             # underscore template extractor for django-babel (internationalization utilities)

requirements/edx/base.txt

@@ -44,6 +44,7 @@ chardet==3.0.4
 git+https://github.com/edx/openedx-chem.git@ff4e3a03d3c7610e47a9af08eb648d8aabe2eb18#egg=chem==1.0.0
 click==7.0                # via code-annotations, user-util
 code-annotations==0.3.2   # via edx-enterprise
+contextlib2==0.5.5
 coreapi==2.3.3            # via drf-yasg
 coreschema==0.0.4         # via coreapi, drf-yasg
 git+https://github.com/edx/crowdsourcehinter.git@a7ffc85b134b7d8909bf1fefd23dbdb8eb28e467#egg=crowdsourcehinter-xblock==0.2
@@ -162,7 +163,7 @@ mock==1.0.1
 git+https://github.com/edx/MongoDBProxy.git@d92bafe9888d2940f647a7b2b2383b29c752f35a#egg=MongoDBProxy==0.1.0+edx.2
 mongoengine==0.10.0
 mpmath==1.1.0             # via sympy
-mysqlclient==1.4.3
+mysqlclient==1.4.4
 networkx==1.7
 newrelic==4.20.1.121
 nltk==3.4.4
@@ -215,7 +216,7 @@ rfc6266-parser==0.0.5.post2
 ruamel.ordereddict==0.4.14 ; python_version == "2.7"  # via ruamel.yaml
 ruamel.yaml.clib==0.1.2   # via ruamel.yaml
 ruamel.yaml==0.16.1       # via drf-yasg
-rules==2.0.1
+rules==2.1
 s3transfer==0.1.13        # via boto3
 sailthru-client==2.2.3
 scipy==1.2.1

requirements/edx/development.txt

@@ -59,7 +59,7 @@ click-log==0.3.2
 click==7.0
 code-annotations==0.3.2
 colorama==0.4.1
-configparser==3.7.4
+configparser==3.8.1
 contextlib2==0.5.5
 cookies==2.2.1
 coreapi==2.3.3
@@ -213,7 +213,7 @@ mongoengine==0.10.0
 more-itertools==5.0.0
 moto==1.3.1
 mpmath==1.1.0
-mysqlclient==1.4.3
+mysqlclient==1.4.4
 networkx==1.7
 newrelic==4.20.1.121
 nltk==3.4.4
@@ -290,7 +290,7 @@ rfc6266-parser==0.0.5.post2
 ruamel.ordereddict==0.4.14 ; python_version == "2.7"
 ruamel.yaml.clib==0.1.2
 ruamel.yaml==0.16.1
-rules==2.0.1
+rules==2.1
 s3transfer==0.1.13
 sailthru-client==2.2.3
 scandir==1.10.0

requirements/edx/testing.txt

@@ -57,8 +57,8 @@ click-log==0.3.2          # via edx-lint
 click==7.0
 code-annotations==0.3.2
 colorama==0.4.1           # via radon
-configparser==3.7.4       # via entrypoints, flake8, importlib-metadata, pylint
-contextlib2==0.5.5        # via importlib-metadata
+configparser==3.8.1       # via entrypoints, flake8, importlib-metadata, pylint
+contextlib2==0.5.5
 cookies==2.2.1            # via moto
 coreapi==2.3.3
 coreschema==0.0.4
@@ -206,7 +206,7 @@ mongoengine==0.10.0
 more-itertools==5.0.0     # via pytest
 moto==1.3.1
 mpmath==1.1.0
-mysqlclient==1.4.3
+mysqlclient==1.4.4
 networkx==1.7
 newrelic==4.20.1.121
 nltk==3.4.4
@@ -281,7 +281,7 @@ rfc6266-parser==0.0.5.post2
 ruamel.ordereddict==0.4.14 ; python_version == "2.7"
 ruamel.yaml.clib==0.1.2
 ruamel.yaml==0.16.1
-rules==2.0.1
+rules==2.1
 s3transfer==0.1.13
 sailthru-client==2.2.3
 scandir==1.10.0           # via pathlib2